Dive in! It’s Freshwater Dolphin Day!
FACT: The Dolphins are the first to complete a perfect 14–0 regular season AND win the Super Bowl in 1972. They are also… wait, we’re not here to talk about the NFL, our actual topic is about freshwater dolphins!
October 24 is when we celebrate International Freshwater Dolphin Day¹. While most dolphin species live exclusively in marine environments, some are known to inhabit freshwater habitats² — this small group is what the celebration is for, to bring attention to their existence and encourage their continued conservation.
Dolphins form part of the marine mammals group, animals from Class Mammalia (like us, humans!) which can live in water. You can think about it like this: millions of years ago, dolphin ancestors used to be terrestrial animals but as they encountered environmental challenges that favored traits suited for an aquatic lifestyle, natural selection ran its course and those animals evolved into the dolphins that we know of today³. One trait of significance is osmoregulation⁴, which is the ability to balance the concentration of salt and water in the body. Freshwater dolphins are remarkably skilled in osmoregulation⁵ and that’s what allows them to thrive in riverine habitats.
There is a fascinating species called Sotalia fluviatilis or more commonly known as tucuxi [too-koo-he], found in the Amazon River in Brazil. Visually, they sort of look like the famous common bottlenose dolphin (Tursiops truncatus) but smaller, and they distinguish themselves by having a pinkish underbelly. They also tend to form big groups from one to six individuals, even up to twenty. You can find them performing maneuvers dolphins are known for, like leaping out of the water, surface-rolling, and even somersaulting⁶!
IUCN lists the tucuxi as endangered with a decreasing population trend⁷, and while the Brazilian government protects these species under law⁶, its enforcement will always be put into question. With their natural habitat in close proximity to human settlements, it’s even more of a challenge to defend these captivating creatures from the threat of pollution, habitat destruction, and human pressures⁸.
By bringing to light these adorable sea creatures, SeaLifeBase hopes to inspire the current and next generation to go out and support programs and initiatives that help protect the tucuxi and the rest of the freshwater dolphins.
Here’s a more relevant dolphin fact: if you want to learn more about dolphins or other marine mammals, head on over to SeaLifeBase and take a dive into their wonderful watery world!
Written by: Jasper Mendoza, Research Assistant
If you have more information on dolphins and other non-fish organisms, we’ll be happy to have you as one of our collaborators. Let us know by sending us an email or visiting our Facebook page.
[1] IUCN — SSC Cetacean Specialist Group. (27 October 2023). 24th October is Freshwater Dolphin Day! Retrieved from: https://iucn-csg.org/24th-october-is-freshwater-dolphin-day-2/.
[2] Cassens I, Vicario S, Waddell VG, Balchowsky H, Van Belle D, Ding W, et al. Independent adaptation to riverine habitats allowed survival of ancient cetacean lineages. Proceedings of the National Academy of Sciences. 2000 Oct 10;97(21):11343–11347. doi: 10.1073/pnas.97.21.11343.
[3] Thewissen JGM, Cooper LN, George JC, Bajpai S. From Land to Water: the Origin of Whales, Dolphins, and Porpoises. Evolution: Education and Outreach. 2009 Apr 16;2(2):272–288. doi: 10.1007/s12052–009–0135–2.
[4] Ridgway S, Venn-Watson S. Effects of fresh and seawater ingestion on osmoregulation in Atlantic bottlenose dolphins (Tursiops truncatus). Journal of Comparative Physiology B. 2010 Jan 1;180(4):563–576. doi: 10.1007/s00360–009–0439–0.
[5] Guo A, Hao Y, Wang J, Zhao Q, Wang D. Concentrations of osmotically related constituents in plasma and urine of finless porpoise (Neophocaena asiaeorientalis): implications for osmoregulatory strategies for marine mammals living in freshwater. Zoological Studies. 2014 Feb 12;53(1). doi: 10.1186/1810–522X-53–10.
[6] Flores PAC, da Silva VMF, Fettuccia D de C. Tucuxi and Guiana Dolphins. Encyclopedia of Marine Mammals. 2018;1024–1027. doi: 10.1016/B978–0–12–804327–1.00264–8.
[7] Trujillo F, Vera da Silva, Martin A, Fettuccia D, Louzamira Bivaqua. IUCN Red List of Threatened Species: Sotalia fluviatilis. IUCN Red List of Threatened Species. Name; 2020. Available from: https://www.iucnredlist.org/species/190871/50386457.
[8] Campbell E, Alfaro-Shigueto J, Aliaga-Rossel E, Beasley I, Briceño Y, Caballero S, et al. Challenges and priorities for river cetacean conservation. Endangered Species Research. 2022 Sep 29;49:13–42. doi: 10.3354/esr01201.
